Just Eat is set to munch its way into the FTSE 100 Index as Merlin Entertainments bows out when the latest market reshuffle is announced on Wednesday.

The online takeaway firm has seen shares jump 43% over the past year, with relentless revenue growth and a string of deals keeping its stock in demand.

The company’s heady rise has pushed its stock market value to £5.5 billion, outstripping supermarket giant Sainsbury’s (£5 billion) and in line with no frills airline easyJet.

A promotion to the top flight would be another bright spot for the firm after seeing its £240 million takeover of rival Hungryhouse given the green light by the Competition and Markets Authority (CMA) earlier this month.

Nicholas Hyett, equity analyst at Hargreaves Lansdown, said: “Reshuffles in and out of the FTSE 100 are somewhat symbolic but can highlight companies whose stars are in the ascendancy, Just Eat being a good example having only floated a little over three years ago.

“It might take payments by card, but when it comes to shareholders, Just Eat, like all good online businesses, is a cash machine.

“Hectic lifestyles mean more meals are bought in rather than cooked at home, which keeps underlying demand firm.

“Customers are fast adopting online ordering as their default order route and Just Eat has been growing orders and revenues at a rate of knots.”

In a contrast of fortunes, Alton Towers owner Merlin Entertainments is expected to be demoted to the FTSE 250 after enduring a stock price slump and weaker trading following a series of UK terror attacks.

The group behind Madame Tussauds and the London Eye has seen visitor numbers tail off in response to the heightened UK threat level, with the blame also being pinned on poor late summer weather across the UK and northern Europe.

Merlin, which dismissed takeover talks with SeaWorld last month, has seen its share price fall by a third since it peaked at 537p in May this year.

Mr Hyett added: “All tourism businesses are subject to the weather, and we already knew terrorist attacks in one of Merlin’s most important destinations were impacting performance.

“However third-quarter results, which cover the crucial summer season, were worse than many had expected. News that tough trading conditions in London are set to continue is also very unwelcome.

“It would be a mistake to write Merlin off though, the group has a portfolio of fundamentally attractive assets and brands that we feel remain attractive to the public in the long term.”

Defence firm Babcock International and pharmaceutical giant Mediclinic are expected to make up the trio of demotions to the second tier, with health and safety sensor maker Halma and packaging firm DS Smith leaping into the top flight.